As radar devices, conventionally, there have been known those disclosed in Patent Documents 1 and 2, for example.
A radar device disclosed in Patent Document 2 is so constructed that the following is implemented: light receiving unit (photodiode) is placed in an enclosure that constructs an illuminating lamp (headlight); reflected light reflected by a reflective object is reflected by a reflector that constructs the headlight; and it is further reflected by a second reflector and received by the receiving unit. More specifically, the reflected light reflected by the reflective object is received by the receiving unit through a reflector as a concave mirror.
[Patent Document 1] JP-A-2001-12943
[Patent Document 2] JP-A-2002-236178
Attempts have been made to detect light in a wide angular range with the aim of expanding a range of detection or lengthening a detection distance. To do this with the construction disclosed in Patent Document 1, it is required to increase the diameter of a condenser lens if its shape is unchanged. With respect to condenser lenses, lens aberration need be taken into account as well. To ensure a desired lens effective diameter, it is required to further increase the diameter of the condenser lens. This results in an increased physical size of a light receiving optical system (radar apparatus).
In the construction disclosed in Patent Document 2, meanwhile, a reflector as a concave mirror is used in place of a condenser lens. Therefore, a problem of aberration does not arise, and the physical size of the light receiving optical system can be accordingly reduced. However, the construction disclosed in Patent Document 2 involves another problem. To detect light in a wide angular range, it is required to increase the size of the mirror if its shape is unchanged. This increases the physical size of the light receiving optical system (radar apparatus). In the construction disclosed in Patent Document 2, light receiving unit is disposed in proximity to a light source in the enclosure that constructs an illuminating lamp. Therefore, there is the possibility that the temperature of a light-sensitive element is raised, and the characteristics of the element are degraded (the reliability of the light-sensitive element is degraded).